Using a multi-functional peripheral equipment (MF) as a function-expanded recording apparatus, original data of text and image data are stored in an image storage device. When original data is printed as a document on print sheets, it can be converted into vector data which can be edited. This vector data can be re-edited and printed. However, easily editable vector data not only allows easy falsification but also poses a copyright protection problem. Therefore, a security level must be set for each vector data.
As a method of setting the security level, for example, a method of embedding information such as a digital watermark or the like which cannot be perceived by the human being has been proposed. Also, as a digital watermark technique, a method of computing the wavelet transforms of image data, and embedding a digital watermark by exploiting redundancy in the frequency domain (Japanese Patent Laid-Open No. 2000-106624 or the like is known.
However, even when security information is embedded as a digital watermark, if the security level is changed after original data (or vector data) is printed, it is impossible to change the security level of the printed document. Therefore, when vector data is generated from the printed document, vector data with a low security level is obtained. For this reason, even though the security level of original data (or vector data) is increased, newly generated vector data can be edited and printed.